How to use Variable Frequency Drive (VFD) Payback& ROI Calculator
- Enter Rated motor full-speed input power (kW) and adjust the options as needed.
- Run the tool and inspect its results, evidence and limitations.
- Copy or download the result, then verify it against the actual website, source data or business records.
Try a concrete example
A 37 kW fan running 6000 hrs/yr retrofitted from damper throttling to VFD saves 84,391 kWh/yr (43.1%), saving $12,659 annually. A $4,200 investment breaks even in 3.99 months with a 10-year NPV of $80,740 and 54.8 metric tons CO₂ offset.
How to interpret results
Applies cubic fan affinity laws (P ∝ N³) across weighted operating duty cycles with discounted cash flow (DCF) modeling to generate reliable energy audit business cases.
Frequently asked questions
Why do variable frequency drives (VFDs) achieve massive energy savings?
Centrifugal fans and pumps follow the affinity laws: flow is proportional to speed (Q ∝ N), pressure to speed squared (P ∝ N²), and power to speed cubed (P ∝ N³). At 80% speed, power drops to 51.2%, cutting energy use by half.
Why is damper throttling inherently inefficient?
Throttling dampers run the motor at full speed while creating artificial flow resistance. The wasted mechanical energy converts directly to air turbulence, aerodynamic hiss, and dissipated heat.
How much electrical power is lost inside the VFD itself?
Modern IGBT inverters operate between 96%~98% efficiency, with 2%~4% heat loss. This calculator conservatively includes drive electrical loss (default 3%) for accurate payback projections.
What additional benefits does a VFD retrofit deliver beyond lower electric bills?
VFDs provide soft-starting, eliminating 6x inrush current surges and water hammer, extending motor winding and mechanical seal lifespans while reducing operating sound levels.